title: Characteristics of major Escherichia coli reductases involved in aerobic nitro and azo reduction.
abstract: OBJECTIVE
  Escherichia coli is able to reduce azo compounds such as methyl red (MR) and nitro compounds such as 7-nitrocoumarin-3-carboxylic acid (7NCCA). The aim of this study was to clarify the specificity of the major E. coli reductases.
  
  
  RESULTS
  Enzymatic assays with pure enzymes obtained after cloning, overproduction and purification under native or denaturing conditions were performed on three enzymes: AzoR, NfsA and NfsB. Their dependence on putative cofactors such as flavin mononucleotide (FMN), NADH and NADPH was studied as well as the reductase capacity of E. coli mutants depleted for one, two or three of the corresponding genes.
  
  
  CONCLUSIONS
  AzoR was able to reduce both MR and 7NCCA, whereas NfsA and NfsB could only reduce the nitro compound. AzoR and NfsB were strictly FMN dependent in contrast to NfsA. At a low oxygen concentration, the three proteins were not mandatory for azo reduction and nitro reduction, but in optimal aerobic conditions, azoR was essential for MR reduction, and an nfsA/nfsB combination was important for 7NCCA reduction. Overexpression of azoR gene was able to compensate for the loss of nfsA and nfsB under aerobic conditions.
  
  
  CONCLUSIONS
  These data provide new insights into the substrate specificity of major E. coli nitroreductases and demonstrate that oxygen is an important parameter to take into account in studies of nitroreductase activity.
authors.affiliation: BioMérieux, La Balme les Grottes, France; CIRI-U1111 INSERM- UMR5308 CNRS-UCBL-ENSL, Université de Lyon, Université Lyon 1, Villeurbanne, France.
authors.forename: C
authors.initials: C
authors.lastname: Mercier
authors.forename: V
authors.initials: V
authors.lastname: Chalansonnet
authors.forename: S
authors.initials: S
authors.lastname: Orenga
authors.forename: C
authors.initials: C
authors.lastname: Gilbert
mesh_terms: D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D005486:Flavin Mononucleotide / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D009601:Nitroreductases / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D029968:Escherichia coli Proteins; D005486:Flavin Mononucleotide; D009247:NADH, NADPH Oxidoreductases; C116053:NfsA protein, E coli; C116054:NfsB protein, E coli; D009601:Nitroreductases; C019759:azobenzene reductase
keywords: AzoR; Escherichia coli; NfsA; NfsB; aerobic; anaerobic; azoreductase; nitroreductase